The epoch making discoveries of the roentgen rays by Roentgen and of radium by the Curies have lead rapidly to much knowledge of vital processes and to the alleviation of disease. One of the must useful clinical applications of these radiations is in the therapy of cancer. The application of radio-active substances does not always result in destruction of the tumor, but their beneficial effects are such as to warrant the search for a means of increasing their destructive properties. It has been suggested that this may be accomplished by introducing into the tissue some substance to augment the production of secondary radiation. Lead, among other substances, has been tried in the belief that it enters cancer tissue and young cells more readily than normal tissue or adult cells.
For determining the effect of irradiation on tissues, with and without the presence of substances causing secondary radiations, animal cancer transplants